The exemplary embodiments described herein relate generally to semiconductor devices and methods for the fabrication thereof and, more specifically, to structures and methods for controlling the formation of junction defects in lateral bipolar junction transistors.
A bipolar junction transistor (BJT) is a semiconductor device comprising three sections of semiconductor material arranged to alternate between P-type and N-type, the sections of semiconductor material forming a base, an emitter, and a collector, thus resulting in a three-region device having an emitter region, a base region, and a collector region having two P-N junctions with one P-N junction being between the emitter and the base and the other P-N junction being between the collector and the base. Each bipolar junction transistor is thus classified as either PNP or NPN according to the arrangement of the P-type material and N-type material. An NPN BJT has an N-type emitter, a P-type base, and an N-type collector, and a PNP BJT has a P-type emitter, an N-type base, and a P-type collector. The function of a BJT is to amplify current, i.e. the collector current (output signal) is larger than the base current (input signal). In a lateral BJT, the base is located between emitter and the collector channels, with the emitter/base junction and the collector/base junction being formed between laterally arranged components.
Germanium may be used in the fabrication of lateral BJTs and can offer high cut off frequencies in both NPN- and PNP-types of BJTs. However, controlling the doping of the emitter/base junction and the collector/base junction using regular ion-implant techniques may be difficult due to insufficient depth control of the implantation, which may result in the obtained lateral and vertical profiles being non-uniform.
Methods of growing faceted epitaxial layers to define the emitter and the collector followed by a recess and re-growth of the epitaxial layers to form channels have been used. In using epitaxial methods on lateral BJTs, however, any non-ideal interface between the epitaxial layers and the germanium surface may be problematic. Such problems may be more prevalent in germanium channel devices as opposed to silicon channel devices since the germanium generally does not tolerate the temperatures of an epitaxial pre-bake process due to the germanium having a lower melting point than silicon. Therefore, in germanium channel devices subjected to the epitaxial pre-bake process, interfaces between the emitter channel and the base as well as interfaces between the collector channel and the base may be less than optimal.